Electrical translation device, including semiconductor



Oct. 12, 1954 J. R. HAYNES 2,691,736

ELECTRICAL TRANSLATION DEVICE, INCLUDING SEMICONDUCTOR Filed Dec. 27,1950 lNl EN TOR J. RxHA VNES ATTORNEY Patented Oct. 12, 1954 orricELECTEi-IGAL TRANSLATION DEVICE, KNOLUDING SEMICQNDUCTGR ApplicationDecember 27, 1950, Serial No. 202,885

(Gil. 250-211) 16 Claims. 1

This invention relates to electrical translation devices employingsemiconductors as their active elements.

The electrical characteristics of semiconductive materials such assilicon and germanium are largely determined by small traces ofimpurities or slight mechanical defects which are present on thesurfaces or within the bodies of the materials. A pure crystal ofsilicon or germanium is made up of a cubic lattice in which each atomhas four valence electrons, all of which are bound in the lattice. Thepresence of what is termed significant impurities disrupt the latticestructure. These impurities are of two different types; those designateddonor impurities which, upon replacing an atom in a crystal lattice,supply more than the needed four valence electrons, and those designatedacceptor impurities which supply less than the needed four valenceelectrons. The former type supplies unbonded. electrons which serve asnegative mobile charge carriers, and the latter, electron deficienciesor holes which serve as positive mobile charge carriers. Asemiconducting material in which conduction by holes normally occurs isidentified as P type, whereas the type in which the principal conductionoccurs by electrons is identified as N type.

One type of semiconductive translator relies principally for itsoperation on the injection of they are injected and also add currentcarriers which flow to an electrode identified generally as a collector,which is biased in the reverse or low conductivity direction withrespect to the semiconductive body. Semiconductive triodes, whereincarriers of a type opposite those ordinarily present in the body areinjected from one electrode known as an emitter to modify the currentflow in a collector circuit, are shown in several applications includingapplication Serial No. 33.4%, filed June 17, 1948, by J. Bardeen and W.H. Brattain, now Patent 2,524,935, issued October 3, 1950, andapplication Serial No. 50,894, filed September 24, 1948, by J. Haynesand W. Shockley, now Patent 2,600,500, issued June 17, 1952. take, theabsorption of light by germanium results in free electron-hole pairs;and the charge is separated and collected. as a result of an electricfield created by the collector. This type is disclosed in applicationSerial No. 85,788 of J. N.

In another form which these units may Z Shive, field April '6, 1949, nowPatent 2,560,608, issued July 17, 1951.

In the above and related types of devices the operating characteristicsare controlled to a large extent by the tendency of the injectedcarriers to recombine with the carriers of opposite sign, therebyeffectively removing them from thematerial. Thus, in a unit employing anN-type semiconductive body, wherein the normal carriers are electrons,the injected holes may'combine with, or be filled by electrons beforethey reach the collector. If No is the number of holes per unit volume,injected at a given time, let us say, 15:0, the number of these holeswhich will remain after a time t=ti is given by the equanon N=N e whereu is called the decay constant the reciprocal of which is known as themean lifetime of the injected holes.

This tendency toward recombination is present in two forms, volumerecombination, and surface recombination, which as the names imply occurwithin the volume of the material and at the surface thereof,respectively, and may be represented by the formula v='1 |1/ where 1/ isthe effective decay constant, 11 is the volume decay constant, and v isthe surface decay constant.

The semiconductor structures of the types described require asubstantial lifetime for the injected carriers, that is, that the holesor electrons persist in an unrecombined state in the semiconductor for asufficient time to perform the tasks required of them.

In consequence of this, a large amount of effort has been expended inattempts to increase the mean life of injected carriers in germanium.Inasmuch as the carriers recombine on the surface, as well as in thevolume of germanium, both rates of recombination have been investigated,with the result that the mean lifetime of carriers in the volume ofgermanium has been increased from the order of 20 microseconds to theorder of 300 microseconds; and surface decay constant has been reducedfrom values of the order of 1000 centimeters per second to less than 80.For a more complete understanding of the various relations discussed inthis specification, the reader is referred to chapter 12 of Electronsand Holes in Semiconductors, by W. Shockley, D. Van Nostrand and Sons,1950.

While such increases in carrier lifetimes are desirable, applicant hasperceived that they are ften accompanied by a significant increase inundesirable effects which he attributes to unwanted or spurious carrieremission. Emission from any electrode, except an emitter, is unwanted,but may nevertheless occur in one degree or another depending on thepotential of the electrode relative to the semiconductive body. Thecarriers so emitted tend to decay or recombine, and in manycircumstances they are of no practical significance, but in longlifetime material they may presist long enough to reach, and minglewith, the wanted carriers, thereby impairing operations.

In a transistor of the type described, for eX ample, in Patent2,524,035, which has emitter and collector point contact electrodes incontact with one surface of a semiconductor body of N-type germanium,and a base electrode making low resistance contact with another surfacethereof, if the base electrode is even slightly positive with respect tothe block, it acts as a second source of positive carriers or holeswhich flow toward the collector in addition to the carriers from theemitter. Since the flow of these unwanted holes from the base electrodeis not modulated in accordance with signal currents, distortion iscaused in the signal output of the collector in so far as such unwantedholes reach the collector in suhstantial volume.

It is therefore a principal object of this invention to improve theoperation of semiconductor translators, specifically by reducing theeffect of unwanted carriers injected from certain of the electrodes.

This and other objects of the invention, which will be apparenthereinafter, are achieved in a semiconductor device in which a portionof the semiconductive body adjacent an electrode acting as a source ofunwanted carriers is arranged to have a high effective decay constant soas to decrease the mean lifetime of such unwanted carriers selectivelyby a significant factor.

Depending on the circumstances, either the surface or the bulk of theaforesaid body portion (or both surface and bulk) may be treated toincrease the decay constant for the purposes of the invention. Severalmethods for producing both high surface and volume decay constants aredescribed in detail hereinafter.

A high surface decay constant may be brought about mechanically bysand-blasting the surface of the body portion or by various chemicalmeans. These include boiling the semiconductor sample in watercontaining metallic ions, or placing the sample in a sol of antimonyoxychloride in which the sample is given a negative potential,attracting antimony ions. The portion of the semiconductor sample fromwhich it is desired to withhold treatment is given a temporaryprotective coating.

Several ways are also described for achieving high volume recombinationconstants. These include heating and quenching the aforesaid bodyportion, or bombarding the same with high energy particles such as alphaparticles, deuterons and neutrons. The methods described may be appliedto different types of semiconductor structures described which includetransistor triodes of the conventional and filamentary types, aphototransistor, and also a rectifier.

Other objects or features of the invention Will be apparent in the studyof the specification hereinafter and the drawings, in which:

Fig. 1 represents an amplifier including a filamentary transistor inwhich a substantial portion of the surface adjacent one of the baseelectrodes has been treated in accordance with the teachings of thepresent invention.

Figs. 2 and 3 represent circuits including a transistor triode and aphototransistor, respectively, which have been treated in accordancewith the teachings of the present invention; and

4 represents a rectifier in which a body portion adjacent the lowresistance contact has been treated in accordance with the presentinvention.

As pointed out above, the undesirable effects produced by unwantedcarrier emission in a semiconductor translating device are substantiallyreduced in accordance with the present invention by recombining theunwanted carriers before they can reach the collecting area.

Several illustrative embodiments of the invention are shown in thedrawings each of which includes a semiconductor body treated forunwanted carrier suppression, in accordance with one of the techniquesto be described hereinafter.

Fig. l of the drawings shows the operating circuit connections for asemiconductor amplifier including a filamentary transistor such asdisclosed in Fig. 1, of Patent 2,608,500, supra. The germaniumsemiconductor body of this structure is assumed to have been treated bysand blasting or one of the other methods for reducing the recombinationconstant adjacent the base electrode.

Although the various means for increasing carrier recombination whichare described hereinafter may often be used interchangeably, the choiceof whether to use surface or volume recombination or a combination ofthe two depends on the particular transistor structure considered, andwhether the mobile charge carriers travel near the surface or at a depthin the semiconducting block.

Referring now in detail to Fig. 1, the translation device showncomprises a body lfii of semiconductive material of one conductivitytype throughout, and having ohmic connections, terminals or contactingmeans Hit, 103 at its opposite ends which may comprise, for example,coatings of rhodium electroplated on the body to form non-rectifyingjunctions therewith. Connected directly between the terminals 593, M3 isa direct-current source Hi, such as a battery, which supplies thebiasing field for producing the current In threading the body it!longitudinally. A contact point HM, for example, of tungsten or Phosphorbronze, engages the body HJI near one end thereof and is connected tothe terminal 33 through a biasing source H31 in series with thesecondary of the input transformer I06, which may be either resistive orinductive. A second contact point I 05 which, for example, may also beof tungsten or Phosphor bronze, engages the body I0! in a region removedfrom the contact IM and adjacent the other end of the body. Point I05 isconnected to the terminal 13' through a biasing source I89 in serieswith the primary coil of the output transformer l H] which, like theinput impedance I06, may be either resistive or inductive.

If, for example, the body Hli is of high back voltage N-type germanium,the polarities of the potential sources lill, H! and R29 are as shown inFig. l. The contact it serves as the emitter; the contact H15 serves asthe collector; and the terminals 33, I03 serve as base electrodecontacts. Specifically, the terminal I63 is connected to the positiveside of the source Hi. The emitter Jill! is biased .to'a sufiicientpositivemotential with respect to the terminal its so that positivecurrent =flows from the emitter 1114 into the body Hi1; -;and the:collector M35 is biased negatively with respect to the terminal this byconnection to source 169. The direction of current flow in the externalcircuit asrs'hown by the arrows in theemitterand collector circuits ofFig.1. If the body :HM isof'P-type material, the polarities of thesources WI, "lDEL-and HI will be reversed. In general, the bias ontheemitter 'lzlbi-shouldbe low, for example, of the orderof-OJ volt; andthe bias on =the-rciollector "1585 should berrelatively large, of theordercofrsome tolGOvolts.

As has been pointed out :hereinbefore, if the body Jill] :is -.ofN-itypeJmateriaI, 'holes are "injec'ted into the body at the emitter NMand flow toward thercolle'ctor Hi5, thereby tending toeffect modulation:of the collector-current. The transs'it time "of Tthefholes fromemitter to collector is a function of the distance between themand alsothe biasing or acceleratingfield due to the source Ill. 'The holes (orcarriers) :flow downthegermaniurn rod toward .thelcoll'e'ctor point1i051under the influence or electric FfiEld. with a velocity which isgiven by the mobility .of"the"holes1nultiplied'bythe electricfieldv Inaddition, since the plated electrode I83 on the left is positive withrespect to the semi-conductor block, it also .acts as a source of holeswhich tend 'to flow down the germanium rod producing a large unwantedinjected hole concentration at the collector.

The distortion produced by the injection "of holes from the platedelectrode N33 is substantially reduced by the sand-blasting :or othertechniques to be described hereinafter which are applied 'to the end orthe rod FBI surrounding this electrode. For example, the treated portionis extended inwardly along the length of the rod a 'little over amillimeter from this electrode. In a case where the cross-sectionaldimensions of the rod were of the order of 0.5 of a millimeter, thissand-blasting treatment served to reducethe lifetime of the carriersfrom more than 106 microseconds to approximately 3 microseconds.Further, since the electrical field which .produced in the rod l El bythe current In is less than 10 volts per centimeter, the unwantedcarriers spend more than 6 microseconds in the treated section l 82.Thus .tl1e number of these unwanted carriers is reduced by more than afactor of 1 0 by this device.

In order to prevent effective numbers of unwanted carriers from flowingacross the germanium rod, when using higher electric fields of the orderof volts per centimeter, a long treated section of approximately 3millimeters has been found desirable.

As pointed out in an earlier paragraph, the e'iiective decay constant ina given semiconductive body is the sum of the surface decay constant andthe volume decay constant. Correspondingly, the followin reciprocalrelationship applies to the effective lifetime constant r2 Particularlyin those embodiments in which the carriers travel near the surface ofthe semiconductive material, such as the filamentary transistordescribed in the foregoing paragraphs, the effective lifetime 1 of thecarriers is, to a much larger extent, a function of the surface decayconstant M than of the volume decay constant By the method ofsand-blasting, or

certaln of the nther techniques .to be described, it is;-possible toproduce ia-rsurfac'e decay constant in excess ofv104Ccentimeterspersecond, thereby :reducing the mean-effective.lifetime for carriers, which isof-the orderof 1'00microseconds in long lifetime germanium, tenfoldpor even .a hundredfold.

In determining how large an area'to-treat, one maybe 'guidedby theformula :given in'the early part =0f the specification *relating to theexponentialdecay of carriers vin-semi-conducting materialfwhichisderived by W; Shockley in chapter E2 of Electrons and Holes inSemiconductors, supra.

In the filamentary transistor, in whichthe unwanted carriers .move alongthe semiconductive filament under the impetus 'of an-appliedtelectricalfield, the Formula 2takes-a modifiedform:

a N='N e assuming thevalue approximate 0.1. According to tabular valuesthe exponent it'l M must approximate 23 (4-) Neglecting the volume decayconstant, the surface decay constant may be computed from the followingapproximate formula, which holds true for those structures in which thecross-sectional dimensions are 0.5 of a millimeter or larger:

where Dp is the difius'ion constant, "which is 44 cmF/second for"positive carriers in germanium;

and a and b are the cross-sectional dimensions of the rectangularfilament in centimeters.

Substituting '(5) in "(4) w approx. 0.15 cm. tfiutt) den) Thesecomputations neglect the recombination of carriers in the germaniumsample :before treatment, which is so small in long lifetime germaniumas to introduce an insignificant error in the result. Hence, the lengthfor the treated area surrounding the positive low contact electrode isof the order of 0.15 centimeter.

Approximately 0.2 of a centimeter at one or the other end of the rod issand-blasted to a maximum degree of roughness in a blast of aircontaining carborundum or similar abrasive material, during whichprocess the remaining portions of the body are protected in some manner,such as with a covering of gummed cellulose tape. Following this step, asection nearest that end, having an. approximate length of 0.05 of acentimeter, is plated with rhodium for low resistance contactelectrodes. This leaves about 0.15 of a centimeter of sand-blastedsurface adjacent the positive base electrode to act as a recombinationsurface. The effectiveness of the sand-blasting technique in increasingthe decay constant of a given semiconductive surface depends at leastpartly on the fact that the actual surface area is greatly increased bythe irregularities so produced. The central portion of the germanium rodmay be given the usual treatment to provide long lifetime for carriers,such as disclosed, for example, in application Serial No. 175,648, filedby J. R. Haynes and R. D. Heidenreich, July 24, 1950. One of the methodsdisclosed in the foregoing application for treating a germanium elementto produce longer lifetime of carriers involves immersing the portion tobe treated in a colloidal solution of very fine particles of antimonyoxychloride. The negatively charged colloidal particles are plated ontothe desired portion of the germanium element by cataphoresis, theelement being maintained at a positive potential with respect to thesolution.

A substantial increase in the surface decay constant can also beobtained chemically by electrolytic treatment of a portion of thegermanium sample, such as described above, in a sol of antimonyoxychloride.

For example, a suitable sol for this purpose may be prepared by adding0.2 of a gram of antimony trichloride to 100 centimeters of distilledwater.

The reaction SbClz-l-HzO-e SbOCl+2HCl takes place to produce a whiteprecipitate of SbOCl. In addition to the large precipitated particleswhich settle down, there is produced a colloidal solution of very fineSbOCl. antimony oxychloride dissociates, producing positive ions ofantimony and negative ions of oxygen and chloride. Hence, if thegermanium sample to treated is made negative by a potential of the orderof 1.5 volts with respect to an anode,

which may be copper or some similar metal, the positive ions of metallicantimony are deposited on the germanium surface. This process ispreferably carried on for a period of ten minutes, the duration oftreatment determining the amount of metallic antimony deposited. Duringthis process, those portions of the germanium body from which it isdesired to withhold treatment are coated with a protective agent, suchas polystyrene dissolved in toluene or cerosine wax. After the metallicfilm has beendeposited on the desired portion, the sample can be rinsedin either high purity distilled water or in alcohol, and the protectivecoating dissolved in toluene prior to applying long lifetime treatment,such as previously described, to the remaining portions of the body.During this treatment, the short lifetime portions of the body areprotected with polystyrene paint which is later removed by dissolving intoluene. The germanium body is then In solution, the

a in condition to be associated with its cooperative elements in theunit in which it is to be used.

Another method of obtaining the desired result is by boiling thesemiconductor element to be treated for a period of ten minutes in watercontaining zinc ions, or another significant impurity, having a minimumconcentration of the order of 10 parts per million. After this step,those portions in which it is desired to retain short lifetimecharacteristics are coated with polystyrene dissolved in alcohol, whilethe long lifetime treatment, such as referred to hereinbefore, isapplied to the remaining portions of the body. fhe polystyrene coatingis removed from the short lifetime portions by dissolving it in toluene.

It should be noted that if, instead of surface recombination techniques,volume recombination techniques such as described hereinafter, areapplied to the filamentary transistor structure described, a shortersection of the rod can be treated.

In addition to the embodiment just described, in which the mobilecarriers move through the semiconducting body primarily under the im--petus of an electrical field, there are several other practicalembodiments, such as shown in Figs. 2, 3 and 4 of the drawings, in whichthe motion of the carriers through the body is principally by diffusion.In each case, a section of the germanium in the immediate vicinity ofthe electrode producing the unwanted carriers is treated to provide ashort lifetime for these carriers. This recombination section isindicated in each case by the dotted areas of the schematic drawing.

Fig. 2 shows a semiconductor triode of the type described in detail inJ. Bardeen and W. H. Brattain, Patent 2,52%,035, which may, for example,include a disc-shaped block of germanium 201 about 0.6 of a centimeterin diameter and 0.1 of a centimeter thick processed in accordance withthe disclosure of J. Bardeen and W. H. Brattain, supra, to provide abody of N-type germanium. A first electrode 204, denoted the emitter,comprising a material such as tungsten, copper or Phosphor bronze, makesrectifying contact with the germanium. A second similar electrode 285,positioned close to the emitter, also makes rectifying contact with theboundary surface. Alternatively, this electrode may comprise a smallspot of metal, such as gold, evaporated into the upper surface, throughwhich a central hole or slot has been pressed. A third electrode 2113consists of a contacting metal film such as rhodium which has beenplated onto the N-type body of the germanium. A small positive potentialbias of the order of a few tenths of a volt is applied to the emitterelectrode 2% with respect to the base electrode 203 from the biasingsource 201. A larger negative bias of the order of 40 volts is appliedto the collector electrode 285 with respect to the base electrode 203.Input signals may be applied between the emitter and base electrodesthrough the primary coil of input transformer 206, which may be eitherresistive or reactive. The primary coil of output transformer 2H1 isconnected between the collector and base electrodes. In the disclosureof Bardeen-Brattain, supra, it is pointed out that if P-type germaniumis substituted for N type in the semiconductor block, the device willfunction with the biasing sources in reversed polarity to those shown.

With the biasing voltages given, for suppressing unwanted carriersinjected from the base electrode 202, the treated portion of the block12 NZNDe J by substituting the relationships:

t (transit time of the carriers) distance I E velocity and- Where N =thenumber of mobile charge carriers arriving at the collecting area; N =thenumber of mobile charge carriers emitted; e=the natural logarithmicconstant; l=path distance from the emitting to the collecting area; D=the diffusion constant for positive carriers in the material traversed;and -r=the efiective lifetime of the carriers=% the effective decayconstant for the semiconductor'material. Makingsubstitutions in Equation7, it can be shown that in order to reduce the'number of unwantedcarriers by one-tenth, the path length L through the treated areainterposed between the electrode source of these carriers and theircollecting point should represent approximately two diffusion pathlengths, a diffusion path length being defined as that distancein whichthecarrier concentration attenuates by a factor eassuming there are noadditional'carrier injections. This term is further'defined by Shockley'in chapter'12 of"Electronsand Holes in Semiconductors, cited above.- As"pointed o'ut'before', if the value i No is to approximate one-tenth,then-referring to Equation '7 and the exponential tables,- it is seenthat the value must be slightly greater than 2. Hence; to reduce thenumber of carriers by a factor of about 10, the path length L throughthe treated area should have a length of the order of 2 /D1-, where Dequals the difiusion constant of the medium, and 1- the effectivelifetime of the injected carriers, or alternatively,

where 11 is the effective decay constant;

In the embodiment under description, since the body of the semiconductoris of such thickness that the mobile charge carriers travel at somedepth from the surface, techniques which increase the volume decayconstant, rather than the surface" decay constant, are most effectiveinjreducing the'lifetimes of the unwanted carriers.

In the cases inwhioh' a high volume recom- 10 bination rate is desiredthe following methods have been found suitable.

The simplest of these involves heating the desired portions of thesample under treatment with a small blow torch or in a small inductionfurnace to a temperature greater than 500 C. for a time interval of theorder of seconds. In the case of N-type material the treated sample istested with a thermoelectric tester to determine the depth of the layerwhich has been converted to P type. Successive etches are carried outuntil the surface is shown to be N type. A suitable thermoelectrictesting device for this purpose is disclosed by W. C. Dunlap in theGeneral Electric Review, vol. 52, page 9, 1949.

Another method comprises bombardment of either N or P-type germaniumwith high energy particles, which may include deuterons and protons asproduced in a cyclotron or other nuclear accelerating device, and alphaparticles from natural radioactive substances such as radium orplutonium.

In changing the lifetime of N-type germanium by nuclear bombardment, thedepth and intensity or the change is dependent on the energy of thebombarding particles and the period of exposure of the body to theseparticles. The function of the bombarding particles is to producerecombination centers in the germanium which facilitate the combinationof holes and electrons there in. By exposing the sample for a relativelyshort time, the resistivity of the irradiated section is increased sothat it is possible by this method to reduce the carrier lifetimes toless than a microsecond. In the case of N type germanium care should betaken, however, to prevent the process being carried too far, thuspreventing the conversion of the treated end section from N to P-typegermanium, since the bombarding particles tend to form P-type centers inthe germanium along with the recombination centers. For example, inorder to change the specific resistance of a sample from 3 to-15-ohm-centimeter, thereby causing the mean lifetime of the carriers tobe reduced to less than one microsecond, the sample is exposed for aninterval of approximately fifteen seconds to a beam of high energyparticles, such as 14 m. e. v. deuteronsfrom a cyclotron or othersource, having an intensity of 0.15 microampere per square inch, whichcorresponds to a bombardment by 9X10 deuterons per second per squareinch of the surface area of the exposed sample. The depth of penetrationof the high energy particles, and hence, the thickness of the layeraffected, increases with particle energy. The portion of thesemiconductor structure which it is desired to preservewith' thelifetime characteristics unchanged is covered by a mask of lead or someother material of such thickness and character as to be impervious tothe nuclear bombardment.

In the conventional transistor device described, the treatment describedin accordance with the present invention operates to reduce thecollector current by reducing the carrier injection from the baseelectrode. This serves to increase the percentage modulation of signalsimpressed on the emitter, and reduce distortion from unwanted spuriouseffects caused by injection of carriers at the base.

Fig. 3 shows the application of a recombination section, such asdescribed, to a phot'otransisto'r of the type disclosed in Fig. 1 ofapplication Serial No. 85,788, filed April 6, 1949, by J. N. Shive, nowPatent 2,566,606, issued July 17, 1951. The apparatus illustrated maycomprise, for example, a disc 30% of high back Voltage N-type germaniumproduced, for example, in the manner disclosed in application Serial No.638,351, filed December 29, 19 5, by J. H. Scaff and H. C. Theuerer,no-w Patent 2,602,211, issued July 8, 1952, and having its surfacesetched as disclosed in that application, and application Serial No.44,241, filed August 14, 1943, by J. N. Shive. Advantageously, the unitmay be given an electrical-forming treatment similar to that describedin the S-hive application. In a specific embodiment, the treated andformed wafer 385 may be 0.15 of an inch in diameter, have an over-allthickness of 0.01 of an inch, and a minimum thickness at the pointcontact region of 0.002 of an inch. To serve as a base electrode, anohmic contact 303 is made with the peripheral surface of the disc, whichmay take the form of a rhodium coating electroplated on this surface, oralternatively, a cured silver paste.

The treated portion 302 of the disc is produced by any of the techniquesin accordance with the present invention described hereinbefore forincreasing either the surface or volume decay constants. If, forexample, sand-blasting is used, this treatment preferably takes placebefore the plating-on of the base electrode, the treated portion formingan annular ring extending inwardly a distance of the order of 0.010 ofan inch from the periphery of the plated section for a reduction ofcarrier injection by more than a factor of 10.

The collector electrode 303 is biased negatively with respect to thebase 303 by a potential source 30], across which is connected thepotential divider 312. In the present illustrative example, the biasingpotential may be of the order of 20 to 100 volts. The load resistance3H1, which may assume values of the order of 10,000 to 25,000 ohms, maybe connected between the collector electrode 304 and the base electrode303. Opposite the disc or wafer 30! is a lens 1% i 3, which iunctions toconcentrate light from a source 3 i i upon a restricted region of thesurface of the disc 530i axially opposite the collector 304. The source3H3, which is connected to the input terminal 306, may be, for example,a tungsten filament operated at about 2900 degrees absolute.

The principal purpose in modifying the phototransistor to include arecombination section 302, such as described, is to reduce the currentwhich flows when there are no light signals falling on the germaniumdisc from the source 333, and which is primarily caused by currentcarriers flowing into the germanium disc from the electrode 303, whichis slightly positive with respect to the disc.

In addition to the transistor applications described, the teachings ofthe present invention may also be applied to semiconductor devices of adilferent type, such as rectifiers having only twoelectrodes, one makinghigh resistance con tact with the body, and the other making lowresistance contact therewith.

Such an embodiment is shown in l of the drawings which discloses asimple semiconductor diode of a type well known in the art. In thisembodiment, treatment in accordance with the present invention of theportion surrounding the low resistance electrode contact serves toreduce unwanted hole emission, which has a tendency to establish areverse current through the rectifier, reducing its eiiiciency.Referring to Fig. 4, a germanium body dill, of roughly similardimensions to the germanium body described with reference to Fig. 2,includes a low resistance electrode of rhodium or similar metal platedon one surface thereof, and a high resistance point contact 2135 oftungsten or Phosphor bronze on the opposite surface. The circuit iscompleted through the secondary coil of input transformer 3M, oneterminal of which is connected to the point contact 2%, and the otherterminal of which is connected through load resistor 3H; to the lowresistance terminal The portion 102 adjacent the plated electrode @503is treated as previously described to decrease that portion of thecurrent which is produced by carrier injection from this electrode dueto its intermittently positive potential with respect to the block. Forthis application, one of the types of volume recombination is used, thedimensions of the treated portion being similar to those described withreference to the transistor of Fig. 2.

Although a number of specific embodiments of the present invention havebeen shown and described by way of illustration, it is apparent thatwithin the scope of this invention, there are many possiblemodifications not shown.

What is claimed is:

l. A translation device comprising in combina tion a body ofsemiconductor material, a source of signal current, emitting means incontact with the surface of said body for supplying mobile chargecarriers to said body under control of signal current from said source,contacting means in contact with said block in a position which issubstantially removed from said emitting means, said contacting meanshaving a potential with respect to the body of said block which is ofthe same sign as that of said mobile charge carriers, said contact meansacting as a source of unwanted charge carriers uncontrolled by saidsignal current, a first region of said semiconductor located betweensaid contacting means and a second region which surrounds said emittingmeans, wherein said first region has a decay rate for said mobile chargecarriers, of the order of at least ten times as great as the decay ratein said second region.

2. A translation device in accordance with claim 1 wherein said firstregion has a surface decay constant which is at least of the order of10- centimeters per second.

3. A translation device in accordance with claim 1 in which the volumedecay constant of said first region is at least ten times that of saidsecond region.

4.. A translation device comprising in combination a semiconductive bodyof N-type germanium, a source of signal current, an emitter in contactwith a surface of said body for supplying positive mobile chargecarriers to said body under control of said signal current, a collectorin contact with said body for receiving positive current carriers fromsaid emitter, an electrode making low-=resistance contact with said bodyand having a slightly positive potential relative to said body, wherebysaid electrode acts as a source of additional positive mobile chargecarriers, said body having a first region adjacent said electrode and asecond region surrounding said emitter and collector, wherein said firstregion has a substantially higher decay rate for said current carriersthan said second region.

5. A translation device in accordance with claim 4 wherein said firstregion has a surface decay constant which is of the order of at least 10times that of said second region.

6. A translation device in accordance with claim 4 in which the volumedecay constant of said first region is of the order of at least timesthat of said second region.

7. A translation device comprising in combination a body ofsemiconductive material, a point contact electrode makinghigh-resistance contact with one surface of said body, a secondelectrode making low-resistance contact with another surface of saidbody, the said body having a relatively low decay constant foruncombined current carriers in a first region adjacent said pointcontact electrode, and a relatively higher decay constant for uncombinedcurrent carriers in a second region adjacent said second electrode,wherein said second region extends of the order of at least 2 diffusionlengths along the path of mobile charge carriers emitted from saidsecond electrode and passing through said second region to said firstregion.

8. A translation device in accordance with claim 7 in which said secondregion has a surface decay constant which is of the order of 10centimeters per second.

9. A photoelectric translation device comprising a body ofsemiconductive material having a thin portion between two opposite facesthereof,

. a point contact engaging one face of said body at said thin portion,an ohmic connection to said body at a position spaced from said contact,a substantial region of said body surrounding said ohmic connectionhaving a decay constant which is of the order of at least 10 times thatof the region of said body engaged by said point contact, and means fordirecting a ray of energy against a face of said body opposite saidpoint contact.

10. A translation device in accordance with claim 9 in-which said regionsurrounding said low-resistance contact has a surface decay constantwhich is of the order of at least 10 centimeters per second.

11. Acircuit element which comprises a block of semi-conductor materialpredominantly comprising a given conductivity type,an emitter electrodemaking contact with said block and injecting current carriers of a givenpolarity into said block, a collector electrode disposed in engagementwith the said block to collect current flowing into the block by way ofthe emitter electrode, a base electrode making contact with the body ofthe block to vary the magnitude of said current, wherein said baseelectrode is the source of unwanted current carriers of the samepolarity as the carriers injected by said emitter electrode, and whereina substantial region adjacent said base electrode has a decay constantfor said carriers which is of the order of at least 10 times the decayconstant in the remaining portions of said block.

12. A circuit which comprises in combination a block of semiconductivematerial having a body which is of one conductivity type and a thinsurface layer which is of the opposite conductivity type, an emitterelectrode making contact with the surface layer and injecting currentcarriers of a given polarity into said block, a collector electrodemaking contact with the surface layer and disposed to collect currentspreading from said emitter electrode, a base electrode making ohmiccontact with the body of said block, said base electrode functioning asa source of unwanted current carriers, a region of said block ad-J'acent said base electrode having a decay constant for said currentcarriers which substantially exceeds the decay constant for currentcarriers in the remaining portion of said block, an input circuitincluding a source of biasing current connected between said emitter andbase electrodes, and an output circuit including a load and a biasingsource connected between said collector and base circuits.

13. A signal translating device which comprises in combination anelongated body of semiconductive material, ohmic contacts plated at twospaced positions on said body, a pair of rectifying contacts at twospaced positions on said body intermediate said ohmic contacts, a firstone of said rectifying contacts functioning as a source of injectedcurrent carriers, an input circuit connected between said firstrectifying contact and a first one of said ohmic contacts nearestthereto, said second rectifying contact functioning to collect thecurrent carriers flowing from said first rectifier contact, an outputcircuit connected between the second one of said ohmic contacts and saidsecond rectifying connection, a biasing means connected between saidohmic contacts, and to said rectifying contacts, wherein a substantialregion adjacent said first ohmic contact has a decay constant forcurrent carriers which is substantially larger than that of the portionsof said block adjacent said rectifying contacts.

14. A signal translating device in accordance with claim 13 in whichsaid region surrounding said first ohmic contact has a surface decayconstant of the order of at least 10 centimeters per second.

15. In combination an electrical device comprising a body ofsemiconductive material having mobile charge carriers of predeterminedsign normally in excess therein, a first electrode in ohmic contact withsaid body, a rectifying connection to said body, a circuit connectingsaid electrode and rectifying connection and including an electricalsource such that said electrode is at least intermittently at apotential of said predetermined sign relative to said body, a bodyportion adjacent said first electrode and interposed in the path ofcarriers tending to flow from said first electrode to said rectifyingconnection, said body portion having a decay constant at least 10 timesthat of the remainder of said body and a length of at least 2 diffusionlengths in the direction of said flow.

16. An electrical semiconductor device comprising a body ofsemiconductive material, a base electrode and a rectifying electrode tosaid body, said body comprising two principal portions interposedbetween said two electrodes, of which one is adjacent said baseelectrode, and has an effective decay constant at least 10 times that ofthe other of said body portions.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,402,661 Ohl June 25, 1946 2,502,479 Pearson et a1. Apr. 4,1950 2,502,488 Shockley Apr. 4, 1950 2,544,211 Barton Mar. 6, 19512,561,411 Pfann July 24, 1951 2,570,978 Pfann Oct. 9, 1951

